1. Field of Invention
The present invention relates to wound dressings.
2. The Prior Art
It is desirable to control the condition of a wound to encourage the healing process. One way is to maintain the wound sufficiently moist so as to absorb or to eliminate the formation of dry crusty scar tissue at the wound site. Another way is to absorb fluids and materials exuded from the wound, including dead leucocytes, epidermal and dermal cells.
At the same time, it is desirable to prevent contamination of the wound by external agents, whether bacterial or fungal, which can lead to infection. Examples of wounds to which these factors are relevant are ulcers, traumatic and surgical wounds, burns and tissue donor sites.
Traditionally, wounded tissues have been covered with various ointments and gauzes. However, these treatments do not shield the wound from external contamination, do not sufficiently retain moisture, and gauzes often become embedded in the wound tissue causing damage and pain when wound dressings are changed.
A recent approach has been to use various forms of hydrogels as wound dressings. The term hydrogel refers to water absorbing gel substances of varying rigidity. Hydrogels may be loaded with various liquid or solid substances destined to hasten and facilitate wound healing. Hydrogels of least rigidity are often administered by syringe while more rigid hydrogels are packed in sterile sachets opened immediately prior to disposing the hydrogel on the wound.
One type of hydrogel wound dressing is a hydrogel consisting of alginate fibres. These are now known in the art. For example, U.S. Pat. Nos. 4,960,413, 4,948,575, 5,238,685 and 5,998,692 provide wound dressing materials containing alginate fibres.
Also known is the therapeutic value of sterilised seawater solutions on open wounds. For example, U.S. Pat. No. 5,084,281 provides a method for treating tissue wounds with a seawater solution.
However, there remains a need for an improved hydrogel wound dressing which is malleable, biodegradable and loaded with various components aimed at preventing infection and facilitating wound healing.
In general terms, the invention provides a wound dressing for treating tissue wounds, the dressing comprising a hydrogel matrix including an absorbent fibrous material comprising an alginate salt, said hydrogel matrix being loaded with components comprising:
a hydrocolloid moisture retaining component;
a salt component compatible with the tissue being treated; and
a vulnerary polysaccharide component.
Preferably, the hydrogel dressing of the present invention will also include a further disinfectant component and will be provided in sheets.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that this detailed description, while indicating preferred embodiments of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.
A detailed description of a preferred embodiment of the present invention will now be described for the purpose of illustration.
The wound dressing of the present invention is a hydrogel loaded with various components for hastening and facilitating wound healing while preventing infection. The hydrogel comprises a matrix of absorbent fibrous material comprising an alginate hydrogel, said matrix being loaded with components comprising:
a hydrocolloid moisture retaining component;
a salt component compatible with the tissue being treated;
a vulnerary polysaccharide component; and optionally
a further disinfectant component.
In the present invention, the term xe2x80x9cdisinfectantxe2x80x9d is synonymous with the terms xe2x80x9cantisepticxe2x80x9d and xe2x80x9canti-bacterialxe2x80x9d. Also, the term xe2x80x9cloadedxe2x80x9d refers to components being absorbed in the hydrogel matrix or to components being deposited on the surface of the hydrogel matrix such as by evaporating a solution containing the component.
Also, the weight percentages (wt %), unless otherwise stated are based on the wt % of ingredients used in the process of making the dressing and not those present in the final product. The proportions were established for a process in which approximately 80% water was incorporated. The dressing may however by dried in order to lower the water content which in turn has a direct effect on the concentration of the other ingredients present in the dressing. The final proportion of water present in the dressing will vary according to the cohesiveness and malleability properties sought after which will differ according to the ingredients used and their concentration.
The process for making the dressing and each ingredient of the wound dressing will now be described in further detail.
The framework of the wound dressing is a matrix composed of either sodium or calcium alginate or a combination of both. Alginate is a naturally occurring protein generally extracted from sea weeds. Upon reacting alginate with sodium or calcium species, insoluble fibers are formed. Various proportions of sodium or calcium alginate (different proportions) are possible. This alginate matrix imparts a cohesive structure to the dressing and has mechanical properties suitable for protecting a wound while remaining flexible. The amount of alginate incorporated in the preparation varies from 1% wt to 4% wt according to the type used.
Processes for making alginates salts, sodium or calcium, are well known in the art. For example, such processes are described in GB-A-0415042 and GB-A-0568177. Two main factors are considered in the preparation of the alginate matrix: firstly, the capacity of alginate to react with calcium or sodium species and secondly, the viscosity of the resulting mixture. The viscosity of the resulting mixture (sodium or calcium alginate or a combination thereof) is directly dependent upon the extent of this reaction. The greater the reactivity (salt formation) between alginate and sodium or calcium species, the less alginate is required in the production of the dressing.
The other components of the dressing of the present invention may be advantageously loaded in the hydrogel by absorption of solutions or slurries containing these ingredients or by direct deposition on the external surface of the hydrogel.
One component is a hydrocolloid component which retains moisture in the hydrogel and gives the hydrogel tissue adherence qualities. This is advantageous because moisture in the hydrogel retains the mechanical properties, such as flexibility, of the hydrogel. Tissue adherence is also beneficial since it allows the hydrogel of the present invention to be used directly on wounds without adhesive tape or superimposed bandages. Examples of suitable hydrocolloids are carboxymethylcellulose, pectine and gums. The hydrogel of the present invention will preferably contain about up to 4 to 5% wt of a hydrocolloid other than carboxymethylcellulose, but it is most preferred to keep the hydrocolloid concentration at values less than 1% in order to avoid diminishing the cohesiveness of the hydrogel.
The salt component absorbed in the hydrogel can be selected from sodium, magnesium, silver or other therapeutically acceptable salts or combinations thereof. These salts have advantageous disinfectant properties and various wound healing properties. Preferably, a 4t% wt sodium chloride solution consisting of sterilized sea salt is loaded in the hydrogel. It is however possible to increase the sea salt concentration to levels up to 8 to 10% wt or to keep it as low as 0.9% wt (physiological solution). The latter concentration has diminished anti-bacterial properties when compared to higher concentrations whereas a strongly concentrated solution can cause a burning sensation.
The vulnerary polysaccharide component absorbed in the hydrogel is preferably chitin, chitosane or a chitosane derivative. Chitin and chitosanes incorporate various sought after properties essential in the healing process of wounds. They have absorbent properties for wicking exudates from the wound site, maintain desired humidity levels at the wound site, and have disinfectant as well as anti-neoplastic properties, that is, they favor the organized formation of new cells which in turn leads to the formation of more esthetically pleasing scars. Chitosane derivatives such as carboxymethylchitosane can also be used, however the concentrations and application conditions will be different in accordance with their efficiency and their characteristics. Preferably, the vulnerary polysaccharide component is chitosane and is absorbed in the hydrogel as a 0.5 to about 1% wt solution in a 1 N lactic acid solution. The required concentration can be superior or inferior depending on the resulting viscosity of the chitosane-lactic acid solution and the anti-bacterial efficiency of the chitosane component. A viscosity that is too high renders the absorption of the chitosane component in the hydrogel difficult. One way to overcome this problem is to dip the hydrogel in the chitosane component solution and to have it evaporate on the surface of the hydrogel.
The further disinfectant component can be chosen from a variety of suitable disinfectants, which will not cause wound irritation or systemic toxicity. Preferred disinfectants are organic acids such as citric acid, dilute acetic acid, benzoic acid, proprionic acid and alcohols such as isopropanol or ethanol. Other examples of possible disinfectants are chlorinated phenolics such as xe2x80x9cTCPxe2x80x9d (2,4,6-trichlorophenol); pine disinfectants such as terpineol; biguanides such as chlorhexidine (when mixed with cetrimide), chlorhexidine gluconate or chlorhexidine acetate; surfactants, preferably amphotheric surfactants; aldehydes such as formaldehyde or gluteraldehyde; halogens such as iodine; iodophores (iodine-containing compounds that slowly liberate inorganic iodine) or organic iodine such as polyvidone-iodine; peroxides and other oxygenators; aluminum zinc agents such as aluminum acetate or zinc sulfate; furan derivatives and, finally, quinoline derivatives such as clioquinol. The disinfectant is either loaded by absorption in the hydrogel or by evaporation thereon. The proportion of disinfectant(s) used will of course depend on the chosen disinfectant(s), their strength, activity and toxicity.
Other optional ingredients having wound healing or anesthetic properties can also be added to the formulation. For example, various vitamins and amino-acids could be incorporated in the hydrogel to diminish scarring. Common anesthetics such as novocaine, lidocaine and derivatives thereof could also be incorporated in the hydrogel. The proportion of these optional ingredients will vary according to the advantages and characteristics sought after in the wound dressing.